测试断裂韧度的一类边裂纹平台圆环(盘)试样:数值分析和标定结果

A SERIES OF EDGE CRACKED FLATTENED RING(DISC) SPECIMENS FOR DETERMINING FRACTURE TOUGHNESS:NUMERICAL ANALYSIS AND CALIBRATION RESULTS

提出测试I型断裂韧度的一类新型试样,包括边裂纹平台圆环、边裂纹平台半圆环、边裂纹平台半圆盘,以及它们没有平台的情况,一共6种构型。采用有限元方法标定这一类边裂纹平台(半)圆环(盘)的量纲一化的应力强度因子,分析其变化规律,并给出相应的曲线拟合公式。结果显示,边裂纹(平台)圆环试样量纲一化的应力强度因子–裂纹长度曲线具有先升后降的特殊性质,这使得它们的测试临界点容易从对应的载荷–位移曲线判断和确定,可以方便地测试材料的断裂韧度。边裂纹平台半圆盘也有类似的性质,但试样宜选取较大的平台角,而边裂纹半圆盘和边裂纹(平台)半圆环却没有这种性质。此外,经过初步试验,用边裂纹平台半圆盘和边裂纹平台半圆环试样测得砂岩的断裂韧度,与用国际岩石力学学会建议试样所测结果吻合。

A series of new specimens were proposed for testing the toughness of mode I fractures：flattened ring with edge cracks,semicircular flattened ring with edge cracks,edge cracked semicircular flattened disc,and their counterparts without flattened ends. Finite element method was used to calibrate the dimensionless stress intensity factor of these specimens and analyse and curve fit the variation of the stress intensity factor. The results reveal that for the edge cracked（flattened） ring,the curve of dimensionless stress intensity factor versus dimensionless crack length appear to be ascending succeeded by descending;so the critical point can be identified directly from the corresponding load-displacement curve based on this unique property,bringing convenience for measuring the material′s fracture toughness. The edge cracked flattened semicircular disc also has such property,but wider flattened ends should be chosen. While the edge cracked semicircular disc and edge cracked（flattened） semicircular ring do not have this unique characteristics. In addition,in the preliminary experimental test,the fracture toughness of a sandstone determined with the edge cracked flattened semicircular disc and the edge cracked flattened semicircular ring coincides respectively with the results derived with the specimen suggested by the International Society for Rock Mechanics.